With input from Dr Monica Vasudev

1567:  COVID Survivors May Need Only One Dose of Vaccine

1. Individuals who have recovered from COVID-19 may only need one dose of the Pfizer-BioNTech or Moderna vaccine to develop a sufficient antibody response; however, COVID-naive people need two doses to achieve robust levels of immunity.
2. Researchers at the University of Pennsylvania assessed antibody and antigen-specific memory B cells over time in 33 SARS-CoV-2-naive and 11 SARS-CoV-2-recovered adults who were administered the Pfizer-BioNTech or Moderna mRNA vaccine.
3. Previous COVID-19 mRNA vaccine studies on vaccinated individuals have addressed antibodies more than memory B cells.
4. SARS-CoV-2-naive individuals required two doses for optimal rise in antibodies, especially for neutralizing titers against the B.1.351 variant.
5. Memory B cells, which are specific for full-length spike protein and the spike receptor binding domain (RBD), were primed by mRNA vaccination and identifiable in all SARS-CoV-2-naive individuals following the second vaccine dose. However, the memory B cell response decreased a bit with age.
6. The study is reported in Science Immunology.
7. On the contrary, SARS-CoV-2-recovered individuals had strong antibody and memory B cell responses after the first vaccine dose and there was no further rise in circulating antibodies, neutralizing titers, or antigen-specific memory B cells following the second dose.
8. These data suggest that only a single dose in individuals who have previously been infected with SARS-CoV-2 may suffice to induce antibody and memory B cell responses.
9. Memory B cells are very efficiently primed by these mRNA vaccines
10. These memory B cells strongly correlate with new antibodies after vaccination. 

[SOURCE: https://bit.ly/3mZ7ljx Science Immunology, online April 15, 2021.]

1568: Chinese researchers are investigating the mix of COVID-19 vaccine doses developed by CanSino Biologics and a unit of Chongqing Zhifei Biological Products, reported clinical trial registration data.

A trial that may include 120 individuals will look into the safety and ability to incite immune response of a dose of CanSinoBIO Ad5-nCoV treatment, followed by a dose of ZF2001 from Anhui Zhifei Longcom Biopharmaceutical at 28-day or 56-day interval, according to ClinicalTrials.gov.

Both vaccines are under use in Chinas mass vaccination drive.

CanSinoBIO stated that interim data from overseas Phase III clinical trials demonstrated that its Ad5-nCoV vaccine was 68.83% effective at preventing symptomatic COVID-19 disease two weeks following an injection, while the efficacy was 65.28% four weeks after one dose.

Researchers in China are also conducting trials on a two-dose Ad5-nCoV regimen, as well as an inhaled version of the vaccine.

[Source: Reuters]

Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA